Vulcanized (per)fluoroelastomers are materials with excellent heat-resistance and chemical-resistance characteristics, which are generally used in the manufacture of technical articles such as sealing parts, pipes, oil seals and O-rings in which the leaktightness, the mechanical properties and the resistance to substances such as mineral oils, hydraulic fluids, solvents or chemical agents of diverse nature must be ensured over a wide range of working temperatures, from low to high temperatures.
A continuing need for (per)fluoroelastomers which can be easily processed yielding final parts endowed with improved leaktightness even at low temperatures combined with the outstanding mechanical properties (i.e. stress at break, modulus and elongation at break) typical of fluoroelastomer materials exists.
One of the approaches for improving processability of (per)fluoroelastomers is the use of lubricants and processing aids dispersed in the (per)fluoroelastomer matrix. However, when such lubricants/processing aids are not compatible with the matrix and/or when they possess high volatility or low thermal resistance, in particular when it is used at high concentrations, while processing can be improved, declines in the leaktightness and elongation at break properties (typical of elastic behaviour) are observed.
Perfluoropolyethers have been thus suggested as processing aids, due to their miscibility with the fluoroelastomeric matrix. EP 0222408 A (AUSIMONT SPA) May 20, 1987 discloses vulcanizable compositions of fluoroelastomers based on vinylidene fluoride, comprising a fluoropolyether as processing aid; similarly, U.S. Pat. No. 4,278,776 (MONTEDISON SPA) Jul. 14, 1981 discloses the use of perfluoropolyethers processing aids in VDF-based fluoroelastomers; in particular performances obtained with perfluoropolyether greases consisting of mixtures of an oil and PTFE particles were compared to those of a perfluoropolyether polyamide in curable fluoroelastomer compounds. In all these documents, adjunction of the perfluoropolyether processing adjuvant was found to be accompanied by a significant reduction of hardness and mechanical properties (modulus). Also, these materials, due to their inherent volatility, undergo migration phenomena and could exude from the cured parts in high temperature operating conditions, so that failures occur and performances of said parts are significantly affected. Finally these materials do not possess outstanding stiction (otherwise known as static friction) properties.
There is thus still a need in the art for (per)fluoroelastomer compositions possessing improved processability and still possessing outstanding sealing properties both at low and high temperatures, combined with outstanding mechanical properties (i.e. modulus and hardness) and outstanding stiction properties.
These stiction properties are of particular interest e.g. for the use of cured parts derived from (per)fluoroelastomer compositions in semiconductors manufacturing devices, both for static applications, wherein disassembly of the device is made easier and for dynamic applications, for instance when used for door sleeves, wherein low stiction values are of interest for enabling relative movement of the sealant and the substrate which is contacted to, with no risk of damage on the softer (per)fluoroelastomer article when detached from harder substrates like ceramic materials or aluminium.